Christopher is 57 years old and Nadia is 6 years old. How many years will it take until Christopher is only 4 times as old as Nadia?
We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Christopher will be $57 + y$ years old and Nadia will be $6 + y$ years old. At that time, Christopher will be 4 times as old as Nadia. Writing this information as an equation, we get: $57 + y = 4 (6 + y)$ Simplifying the right side of this equation, we get: $57 + y = 24 + 4 y$ Solving for $y$ , we get: $3 y = 33$ $y = 11$.